Thanks Underneath The Radar - found the answer on the Easyjet site.
For the benefit of anyone else interested:
"Please note that if you hold a European National JAA licence, you will have to exchange it for a UK JAA licence before you start with us. This is due to training purposes (mainly for our TRE's to be able to sign for the type rating endorsement on your licence). The process for the exchange involves filling an application form, sending copies of your licence and medical certificate along with an administration fee."
As suspected, another pointless paperwork exercise and another excuse to screw us out of our hard earned cash.